This project involves a series of studies focused on the young infant's perception of contingency between behavior and its stimulus consequences. The major objective is to gather parametric information on the ability of infants slightly younger and older than 3 months (the age at which instrumental activity normally appears) to respond to contingencies under conditions which approximate those in the real world; i.e., when his/her behaviors do not always produce contingent stimuli; the contingent stimuli sometimes occur independent of behavior; and there is sometimes a delay between response and stimulus. The effects of partial reinforcement, mixing noncontingent with contingent reinforcement, providing discriminative stimuli, and contrasting social versus nonsocial stimuli will be examined, both in laboratory and relatively long-term home-based experimental situations. In addition, the effects of combinations of partial and noncontingent stimulation and delay of reward will be examined in the laboratory. In combination with observational data on mother-infant interaction currently being analyzed, the findings will provide basic information on the ability of infants to perceive contingencies under natural, and laboratory approximation of natural, conditions.